/*
 * Copyright (C) 2008, 2009 The Android Open Source Project
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *  * Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *  * Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <dlfcn.h>
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <unistd.h>

// Private C library headers.
#include "private/bionic_tls.h"
#include "private/KernelArgumentBlock.h"
#include "private/ScopedPthreadMutexLocker.h"
#include "private/ScopedFd.h"

#include "linker.h"
#include "linker_debug.h"
#include "linker_environ.h"
#include "linker_phdr.h"
#include "linker_allocator.h"

/* >>> IMPORTANT NOTE - READ ME BEFORE MODIFYING <<<
 *
 * Do NOT use malloc() and friends or pthread_*() code here.
 * Don't use printf() either; it's caused mysterious memory
 * corruption in the past.
 * The linker runs before we bring up libc and it's easiest
 * to make sure it does not depend on any complex libc features
 *
 * open issues / todo:
 *
 * - cleaner error reporting
 * - after linking, set as much stuff as possible to READONLY
 *   and NOEXEC
 */

#if defined(__LP64__)
#define SEARCH_NAME(x) x
#else
// Nvidia drivers are relying on the bug:
// http://code.google.com/p/android/issues/detail?id=6670
// so we continue to use base-name lookup for lp32
static const char* get_base_name(const char* name) {
	const char* bname = strrchr(name, '/');
	return bname ? bname + 1 : name;
}
#define SEARCH_NAME(x) get_base_name(x)
#endif

static bool soinfo_link_image(soinfo* si, const android_dlextinfo* extinfo);
static ElfW(Addr) get_elf_exec_load_bias(const ElfW(Ehdr)* elf);

static LinkerAllocator<soinfo> g_soinfo_allocator;
static LinkerAllocator<LinkedListEntry<soinfo>> g_soinfo_links_allocator;

static soinfo* solist;
static soinfo* sonext;
static soinfo* somain; /* main process, always the one after libdl_info */

static const char* const kDefaultLdPaths[] = {
#if defined(__LP64__)
	"/vendor/lib64",
	"/system/lib64",
#else
	"/vendor/lib",
	"/system/lib",
#endif
	NULL
};

#define LDPATH_BUFSIZE (LDPATH_MAX*64)
#define LDPATH_MAX 8

#define LDPRELOAD_BUFSIZE (LDPRELOAD_MAX*64)
#define LDPRELOAD_MAX 8

static char g_ld_library_paths_buffer[LDPATH_BUFSIZE];
static const char* g_ld_library_paths[LDPATH_MAX + 1];

static char g_ld_preloads_buffer[LDPRELOAD_BUFSIZE];
static const char* g_ld_preload_names[LDPRELOAD_MAX + 1];

static soinfo* g_ld_preloads[LDPRELOAD_MAX + 1];

__LIBC_HIDDEN__ int g_ld_debug_verbosity;

__LIBC_HIDDEN__ abort_msg_t* g_abort_message = NULL; // For debuggerd.

enum RelocationKind {
		kRelocAbsolute = 0,
		kRelocRelative,
		kRelocCopy,
		kRelocSymbol,
		kRelocMax
};

#if STATS
struct linker_stats_t {
		int count[kRelocMax];
};

static linker_stats_t linker_stats;

static void count_relocation(RelocationKind kind) {
		++linker_stats.count[kind];
}
#else
static void count_relocation(RelocationKind) {
}
#endif

#if COUNT_PAGES
static unsigned bitmask[4096];
#if defined(__LP64__)
#define MARK(offset) \
		do { \
				if ((((offset) >> 12) >> 5) < 4096) \
						bitmask[((offset) >> 12) >> 5] |= (1 << (((offset) >> 12) & 31)); \
		} while (0)
#else
#define MARK(offset) \
		do { \
				bitmask[((offset) >> 12) >> 3] |= (1 << (((offset) >> 12) & 7)); \
		} while (0)
#endif
#else
#define MARK(x) do {} while (0)
#endif

// You shouldn't try to call memory-allocating functions in the dynamic linker.
// Guard against the most obvious ones.
#define DISALLOW_ALLOCATION(return_type, name, ...) \
		return_type name __VA_ARGS__ \
		{ \
				__libc_fatal("ERROR: " #name " called from the dynamic linker!\n"); \
		}
DISALLOW_ALLOCATION(void*, malloc, (size_t u __unused));
DISALLOW_ALLOCATION(void, free, (void* u __unused));
DISALLOW_ALLOCATION(void*, realloc, (void* u1 __unused, size_t u2 __unused));
DISALLOW_ALLOCATION(void*, calloc, (size_t u1 __unused, size_t u2 __unused));

static char tmp_err_buf[768];
static char __linker_dl_err_buf[768];

char* linker_get_error_buffer() {
	return &__linker_dl_err_buf[0];
}

size_t linker_get_error_buffer_size() {
	return sizeof(__linker_dl_err_buf);
}

/*
 * This function is an empty stub where GDB locates a breakpoint to get notified
 * about linker activity.
 */
extern "C" void __attribute__((noinline)) __attribute__((visibility("default"))) rtld_db_dlactivity();

static pthread_mutex_t g__r_debug_mutex = PTHREAD_MUTEX_INITIALIZER;
static r_debug _r_debug = {1, NULL, reinterpret_cast<uintptr_t>(&rtld_db_dlactivity), r_debug::RT_CONSISTENT, 0};
static link_map* r_debug_tail = 0;

static void insert_soinfo_into_debug_map(soinfo* info) {
		// Copy the necessary fields into the debug structure.
		link_map* map = &(info->link_map_head);
		map->l_addr = info->load_bias;
		map->l_name = reinterpret_cast<char*>(info->name);
		map->l_ld = info->dynamic;

		/* Stick the new library at the end of the list.
		 * gdb tends to care more about libc than it does
		 * about leaf libraries, and ordering it this way
		 * reduces the back-and-forth over the wire.
		 */
		if (r_debug_tail) {
				r_debug_tail->l_next = map;
				map->l_prev = r_debug_tail;
				map->l_next = 0;
		} else {
				_r_debug.r_map = map;
				map->l_prev = 0;
				map->l_next = 0;
		}
		r_debug_tail = map;
}

static void remove_soinfo_from_debug_map(soinfo* info) {
		link_map* map = &(info->link_map_head);

		if (r_debug_tail == map) {
				r_debug_tail = map->l_prev;
		}

		if (map->l_prev) {
				map->l_prev->l_next = map->l_next;
		}
		if (map->l_next) {
				map->l_next->l_prev = map->l_prev;
		}
}

static void notify_gdb_of_load(soinfo* info) {
		if (info->flags & FLAG_EXE) {
				// GDB already knows about the main executable
				return;
		}

		ScopedPthreadMutexLocker locker(&g__r_debug_mutex);

		_r_debug.r_state = r_debug::RT_ADD;
		rtld_db_dlactivity();

		insert_soinfo_into_debug_map(info);

		_r_debug.r_state = r_debug::RT_CONSISTENT;
		rtld_db_dlactivity();
}

static void notify_gdb_of_unload(soinfo* info) {
		if (info->flags & FLAG_EXE) {
				// GDB already knows about the main executable
				return;
		}

		ScopedPthreadMutexLocker locker(&g__r_debug_mutex);

		_r_debug.r_state = r_debug::RT_DELETE;
		rtld_db_dlactivity();

		remove_soinfo_from_debug_map(info);

		_r_debug.r_state = r_debug::RT_CONSISTENT;
		rtld_db_dlactivity();
}

void notify_gdb_of_libraries() {
	_r_debug.r_state = r_debug::RT_ADD;
	rtld_db_dlactivity();
	_r_debug.r_state = r_debug::RT_CONSISTENT;
	rtld_db_dlactivity();
}

LinkedListEntry<soinfo>* SoinfoListAllocator::alloc() {
	return g_soinfo_links_allocator.alloc();
}

void SoinfoListAllocator::free(LinkedListEntry<soinfo>* entry) {
	g_soinfo_links_allocator.free(entry);
}

static void protect_data(int protection) {
	g_soinfo_allocator.protect_all(protection);
	g_soinfo_links_allocator.protect_all(protection);
}

static soinfo* soinfo_alloc(const char* name, struct stat* file_stat) {
	if (strlen(name) >= SOINFO_NAME_LEN) {
		DL_ERR("library name \"%s\" too long", name);
		return NULL;
	}

	soinfo* si = g_soinfo_allocator.alloc();

	// Initialize the new element.
	memset(si, 0, sizeof(soinfo));
	strlcpy(si->name, name, sizeof(si->name));
	si->flags = FLAG_NEW_SOINFO;

	if (file_stat != NULL) {
		si->set_st_dev(file_stat->st_dev);
		si->set_st_ino(file_stat->st_ino);
	}

	sonext->next = si;
	sonext = si;

	TRACE("name %s: allocated soinfo @ %p", name, si);
	return si;
}

static void soinfo_free(soinfo* si) {
		if (si == NULL) {
				return;
		}

		if (si->base != 0 && si->size != 0) {
			munmap(reinterpret_cast<void*>(si->base), si->size);
		}

		soinfo *prev = NULL, *trav;

		TRACE("name %s: freeing soinfo @ %p", si->name, si);

		for (trav = solist; trav != NULL; trav = trav->next) {
				if (trav == si)
						break;
				prev = trav;
		}
		if (trav == NULL) {
				/* si was not in solist */
				DL_ERR("name \"%s\" is not in solist!", si->name);
				return;
		}

		// clear links to/from si
		si->remove_all_links();

		/* prev will never be NULL, because the first entry in solist is
			 always the static libdl_info.
		*/
		prev->next = si->next;
		if (si == sonext) {
				sonext = prev;
		}

		g_soinfo_allocator.free(si);
}


static void parse_path(const char* path, const char* delimiters,
											 const char** array, char* buf, size_t buf_size, size_t max_count) {
	if (path == NULL) {
		return;
	}

	size_t len = strlcpy(buf, path, buf_size);

	size_t i = 0;
	char* buf_p = buf;
	while (i < max_count && (array[i] = strsep(&buf_p, delimiters))) {
		if (*array[i] != '\0') {
			++i;
		}
	}

	// Forget the last path if we had to truncate; this occurs if the 2nd to
	// last char isn't '\0' (i.e. wasn't originally a delimiter).
	if (i > 0 && len >= buf_size && buf[buf_size - 2] != '\0') {
		array[i - 1] = NULL;
	} else {
		array[i] = NULL;
	}
}

static void parse_LD_LIBRARY_PATH(const char* path) {
	parse_path(path, ":", g_ld_library_paths,
						 g_ld_library_paths_buffer, sizeof(g_ld_library_paths_buffer), LDPATH_MAX);
}

static void parse_LD_PRELOAD(const char* path) {
	// We have historically supported ':' as well as ' ' in LD_PRELOAD.
	parse_path(path, " :", g_ld_preload_names,
						 g_ld_preloads_buffer, sizeof(g_ld_preloads_buffer), LDPRELOAD_MAX);
}

#if defined(__arm__)

/* For a given PC, find the .so that it belongs to.
 * Returns the base address of the .ARM.exidx section
 * for that .so, and the number of 8-byte entries
 * in that section (via *pcount).
 *
 * Intended to be called by libc's __gnu_Unwind_Find_exidx().
 *
 * This function is exposed via dlfcn.cpp and libdl.so.
 */
_Unwind_Ptr dl_unwind_find_exidx(_Unwind_Ptr pc, int* pcount) {
		unsigned addr = (unsigned)pc;

		for (soinfo* si = solist; si != 0; si = si->next) {
				if ((addr >= si->base) && (addr < (si->base + si->size))) {
						*pcount = si->ARM_exidx_count;
						return (_Unwind_Ptr)si->ARM_exidx;
				}
		}
		*pcount = 0;
		return NULL;
}

#endif

/* Here, we only have to provide a callback to iterate across all the
 * loaded libraries. gcc_eh does the rest. */
int dl_iterate_phdr(int (*cb)(dl_phdr_info* info, size_t size, void* data), void* data) {
		int rv = 0;
		for (soinfo* si = solist; si != NULL; si = si->next) {
				dl_phdr_info dl_info;
				dl_info.dlpi_addr = si->link_map_head.l_addr;
				dl_info.dlpi_name = si->link_map_head.l_name;
				dl_info.dlpi_phdr = si->phdr;
				dl_info.dlpi_phnum = si->phnum;
				rv = cb(&dl_info, sizeof(dl_phdr_info), data);
				if (rv != 0) {
						break;
				}
		}
		return rv;
}
//调用 soinfo_do_lookup()查找符号的定义 so
static ElfW(Sym)* soinfo_elf_lookup(soinfo* si, unsigned hash, const char* name) {
	ElfW(Sym)* symtab = si->symtab;//符号表
	const char* strtab = si->strtab;

	TRACE_TYPE(LOOKUP, "SEARCH %s in %s@%p %x %zd",
						 name, si->name, reinterpret_cast<void*>(si->base), hash, hash % si->nbucket);
    //通过哈希表在符号表中快速查找 name
	for (unsigned n = si->bucket[hash % si->nbucket]; n != 0; n = si->chain[n]) {
		ElfW(Sym)* s = symtab + n;
		if (strcmp(strtab + s->st_name, name)) continue;//符号名字需相同

		/* only concern ourselves with global and weak symbol definitions */
		switch (ELF_ST_BIND(s->st_info)) {
			case STB_GLOBAL:
			case STB_WEAK:
				if (s->st_shndx == SHN_UNDEF) {//符号未定义
					continue;
				}

				TRACE_TYPE(LOOKUP, "FOUND %s in %s (%p) %zd",
								 name, si->name, reinterpret_cast<void*>(s->st_value),
								 static_cast<size_t>(s->st_size));
				return s;//在 si 中找到符号的定义
			case STB_LOCAL:
				continue;
			default:
				__libc_fatal("ERROR: Unexpected ST_BIND value: %d for '%s' in '%s'",
						ELF_ST_BIND(s->st_info), name, si->name);
		}
	}

	TRACE_TYPE(LOOKUP, "NOT FOUND %s in %s@%p %x %zd",
						 name, si->name, reinterpret_cast<void*>(si->base), hash, hash % si->nbucket);


	return NULL;
}

static unsigned elfhash(const char* _name) {
		const unsigned char* name = reinterpret_cast<const unsigned char*>(_name);
		unsigned h = 0, g;

		while (*name) {
				h = (h << 4) + *name++;
				g = h & 0xf0000000;
				h ^= g;
				h ^= g >> 24;
		}
		return h;
}
//soinfo_do_look()分别在其自身、 预加载库和依赖库中查找符号的定义
static ElfW(Sym)* soinfo_do_lookup(soinfo* si, const char* name, soinfo** lsi, soinfo* needed[]) {
		unsigned elf_hash = elfhash(name);//计算符号的哈希值
		ElfW(Sym)* s = NULL;

		if (si != NULL && somain != NULL) {
				/*
				 * Local scope is executable scope. Just start looking into it right away
				 * for the shortcut.
				 */

				if (si == somain) {
						s = soinfo_elf_lookup(si, elf_hash, name);
						if (s != NULL) {
								*lsi = si;
								goto done;
						}

						/* Next, look for it in the preloads list */
						for (int i = 0; g_ld_preloads[i] != NULL; i++) {
								s = soinfo_elf_lookup(g_ld_preloads[i], elf_hash, name);
								if (s != NULL) {
										*lsi = g_ld_preloads[i];
										goto done;
								}
						}
				} else {
						/* Order of symbol lookup is controlled by DT_SYMBOLIC flag */

						/*
						 * If this object was built with symbolic relocations disabled, the
						 * first place to look to resolve external references is the main
						 * executable.
						 */

						if (!si->has_DT_SYMBOLIC) {
								DEBUG("%s: looking up %s in executable %s",
											si->name, name, somain->name);
								s = soinfo_elf_lookup(somain, elf_hash, name);
								if (s != NULL) {
										*lsi = somain;
										goto done;
								}

								/* Next, look for it in the preloads list */
								for (int i = 0; g_ld_preloads[i] != NULL; i++) {
										s = soinfo_elf_lookup(g_ld_preloads[i], elf_hash, name);
										if (s != NULL) {
												*lsi = g_ld_preloads[i];
												goto done;
										}
								}
						}

						/* Look for symbols in the local scope (the object who is
						 * searching). This happens with C++ templates on x86 for some
						 * reason.
						 *
						 * Notes on weak symbols:
						 * The ELF specs are ambiguous about treatment of weak definitions in
						 * dynamic linking.  Some systems return the first definition found
						 * and some the first non-weak definition.   This is system dependent.
						 * Here we return the first definition found for simplicity.  */

						s = soinfo_elf_lookup(si, elf_hash, name);
						if (s != NULL) {
								*lsi = si;
								goto done;
						}

						/*
						 * If this object was built with -Bsymbolic and symbol is not found
						 * in the local scope, try to find the symbol in the main executable.
						 */

						if (si->has_DT_SYMBOLIC) {
								DEBUG("%s: looking up %s in executable %s after local scope",
											si->name, name, somain->name);
								s = soinfo_elf_lookup(somain, elf_hash, name);
								if (s != NULL) {
										*lsi = somain;
										goto done;
								}

								/* Next, look for it in the preloads list */
								for (int i = 0; g_ld_preloads[i] != NULL; i++) {
										s = soinfo_elf_lookup(g_ld_preloads[i], elf_hash, name);
										if (s != NULL) {
												*lsi = g_ld_preloads[i];
												goto done;
										}
								}
						}
				}
		}

		for (int i = 0; needed[i] != NULL; i++) {
				DEBUG("%s: looking up %s in %s",
							si->name, name, needed[i]->name);
				s = soinfo_elf_lookup(needed[i], elf_hash, name);
				if (s != NULL) {
						*lsi = needed[i];
						goto done;
				}
		}

done:
		if (s != NULL) {
				TRACE_TYPE(LOOKUP, "si %s sym %s s->st_value = %p, "
									 "found in %s, base = %p, load bias = %p",
									 si->name, name, reinterpret_cast<void*>(s->st_value),
									 (*lsi)->name, reinterpret_cast<void*>((*lsi)->base),
									 reinterpret_cast<void*>((*lsi)->load_bias));
				return s;
		}

		return NULL;
}

// Another soinfo list allocator to use in dlsym. We don't reuse
// SoinfoListAllocator because it is write-protected most of the time.
static LinkerAllocator<LinkedListEntry<soinfo>> g_soinfo_list_allocator_rw;
class SoinfoListAllocatorRW {
 public:
	static LinkedListEntry<soinfo>* alloc() {
		return g_soinfo_list_allocator_rw.alloc();
	}

	static void free(LinkedListEntry<soinfo>* ptr) {
		g_soinfo_list_allocator_rw.free(ptr);
	}
};

// This is used by dlsym(3).  It performs symbol lookup only within the
// specified soinfo object and its dependencies in breadth first order.
ElfW(Sym)* dlsym_handle_lookup(soinfo* si, soinfo** found, const char* name) {
	LinkedList<soinfo, SoinfoListAllocatorRW> visit_list;
	LinkedList<soinfo, SoinfoListAllocatorRW> visited;
	visit_list.push_back(si);
	soinfo* current_soinfo;
	while ((current_soinfo = visit_list.pop_front()) != nullptr) {
		if (visited.contains(current_soinfo)) {
			continue;
		}

		ElfW(Sym)* result = soinfo_elf_lookup(current_soinfo, elfhash(name), name);

		if (result != nullptr) {
			*found = current_soinfo;
			visit_list.clear();
			visited.clear();
			return result;
		}
		visited.push_back(current_soinfo);

		current_soinfo->get_children().for_each([&](soinfo* child) {
			visit_list.push_back(child);
		});
	}

	visit_list.clear();
	visited.clear();
	return nullptr;
}

/* This is used by dlsym(3) to performs a global symbol lookup. If the
	 start value is null (for RTLD_DEFAULT), the search starts at the
	 beginning of the global solist. Otherwise the search starts at the
	 specified soinfo (for RTLD_NEXT).
 */
ElfW(Sym)* dlsym_linear_lookup(const char* name, soinfo** found, soinfo* start) {
	unsigned elf_hash = elfhash(name);

	if (start == NULL) {
		start = solist;
	}

	ElfW(Sym)* s = NULL;
	for (soinfo* si = start; (s == NULL) && (si != NULL); si = si->next) {
		s = soinfo_elf_lookup(si, elf_hash, name);
		if (s != NULL) {
			*found = si;
			break;
		}
	}

	if (s != NULL) {
		TRACE_TYPE(LOOKUP, "%s s->st_value = %p, found->base = %p",
							 name, reinterpret_cast<void*>(s->st_value), reinterpret_cast<void*>((*found)->base));
	}

	return s;
}

soinfo* find_containing_library(const void* p) {
	ElfW(Addr) address = reinterpret_cast<ElfW(Addr)>(p);
	for (soinfo* si = solist; si != NULL; si = si->next) {
		if (address >= si->base && address - si->base < si->size) {
			return si;
		}
	}
	return NULL;
}

ElfW(Sym)* dladdr_find_symbol(soinfo* si, const void* addr) {
	ElfW(Addr) soaddr = reinterpret_cast<ElfW(Addr)>(addr) - si->base;

	// Search the library's symbol table for any defined symbol which
	// contains this address.
	for (size_t i = 0; i < si->nchain; ++i) {
		ElfW(Sym)* sym = &si->symtab[i];
		if (sym->st_shndx != SHN_UNDEF &&
				soaddr >= sym->st_value &&
				soaddr < sym->st_value + sym->st_size) {
			return sym;
		}
	}

	return NULL;
}

static int open_library_on_path(const char* name, const char* const paths[]) {
	char buf[512];
	for (size_t i = 0; paths[i] != NULL; ++i) {
		int n = __libc_format_buffer(buf, sizeof(buf), "%s/%s", paths[i], name);
		if (n < 0 || n >= static_cast<int>(sizeof(buf))) {
			PRINT("Warning: ignoring very long library path: %s/%s", paths[i], name);
			continue;
		}
		int fd = TEMP_FAILURE_RETRY(open(buf, O_RDONLY | O_CLOEXEC));
		if (fd != -1) {
			return fd;
		}
	}
	return -1;
}

static int open_library(const char* name) {
	TRACE("[ opening %s ]", name);

	// If the name contains a slash, we should attempt to open it directly and not search the paths.
	if (strchr(name, '/') != NULL) {
		int fd = TEMP_FAILURE_RETRY(open(name, O_RDONLY | O_CLOEXEC));
		if (fd != -1) {
			return fd;
		}
		// ...but nvidia binary blobs (at least) rely on this behavior, so fall through for now.
#if defined(__LP64__)
		return -1;
#endif
	}

	// Otherwise we try LD_LIBRARY_PATH first, and fall back to the built-in well known paths.
	int fd = open_library_on_path(name, g_ld_library_paths);
	if (fd == -1) {
		fd = open_library_on_path(name, kDefaultLdPaths);
	}
	return fd;
}

static soinfo* load_library(const char* name, int dlflags, const android_dlextinfo* extinfo) {//extinfo为空
		int fd = -1;//.so文件的描述符
		ScopedFd file_guard(-1);
		//part 1
		if (extinfo != NULL && (extinfo->flags & ANDROID_DLEXT_USE_LIBRARY_FD) != 0) {
			fd = extinfo->library_fd;
		} else {
			// Open the file.
			fd = open_library(name);//打开so文件
			if (fd == -1) {
				DL_ERR("library \"%s\" not found", name);
				return NULL;
			}

			file_guard.reset(fd);
		}

		ElfReader elf_reader(name, fd);

		struct stat file_stat;
		if (TEMP_FAILURE_RETRY(fstat(fd, &file_stat)) != 0) {//获取.so文件的状态
			DL_ERR("unable to stat file for the library %s: %s", name, strerror(errno));
			return NULL;
		}

		// Check for symlink and other situations where
		// file can have different names.
		//linux 下可以生成文件的链接文件， 这里检查.so 文件是否以不同的名字加载
		for (soinfo* si = solist; si != NULL; si = si->next) {
			if (si->get_st_dev() != 0 &&
					si->get_st_ino() != 0 &&
					si->get_st_dev() == file_stat.st_dev &&
					si->get_st_ino() == file_stat.st_ino) {
				TRACE("library \"%s\" is already loaded under different name/path \"%s\" - will return existing soinfo", name, si->name);
				return si;
			}
		}

		if ((dlflags & RTLD_NOLOAD) != 0) {
			return NULL;
		}

		// Read the ELF header and load the segments.
		if (!elf_reader.Load(extinfo)) {
				return NULL;
		}
		//为 soinfo 分配空间
		soinfo* si = soinfo_alloc(SEARCH_NAME(name), &file_stat);
		if (si == NULL) {
				return NULL;
		}
		si->base = elf_reader.load_start();//加载 so 文件时， mmap 得到的空间的首地址
		si->size = elf_reader.load_size();//ReserveAddressSpace 中开辟的内存空间的大小
		si->load_bias = elf_reader.load_bias();//加载段时的基址， load_bias+p_vaddr 为段的实际内存地址
		si->phnum = elf_reader.phdr_count();//program header 的个数
		si->phdr = elf_reader.loaded_phdr();//program header table 在内存中的起始地址

		// At this point we know that whatever is loaded @ base is a valid ELF
		// shared library whose segments are properly mapped in.
		TRACE("[ load_library base=%p size=%zu name='%s' ]",
					reinterpret_cast<void*>(si->base), si->size, si->name);

		if (!soinfo_link_image(si, extinfo)) {
			soinfo_free(si);
			return NULL;
		}

		return si;
}

static soinfo *find_loaded_library_by_name(const char* name) {
	const char* search_name = SEARCH_NAME(name);
	for (soinfo* si = solist; si != NULL; si = si->next) {
		if (!strcmp(search_name, si->name)) {
			return si;
		}
	}
	return NULL;
}

static soinfo* find_library_internal(const char* name, int dlflags, const android_dlextinfo* extinfo) {
	if (name == NULL) {
		return somain;
	}

	soinfo* si = find_loaded_library_by_name(name);

	// Library might still be loaded, the accurate detection
	// of this fact is done by load_library
	if (si == NULL) {
		TRACE("[ '%s' has not been found by name.  Trying harder...]", name);
		si = load_library(name, dlflags, extinfo);
	}

	if (si != NULL && (si->flags & FLAG_LINKED) == 0) {
		DL_ERR("recursive link to \"%s\"", si->name);
		return NULL;
	}

	return si;
}

static soinfo* find_library(const char* name, int dlflags, const android_dlextinfo* extinfo) {
	soinfo* si = find_library_internal(name, dlflags, extinfo);
	if (si != NULL) {
		si->ref_count++;
	}
	return si;
}

static void soinfo_unload(soinfo* si) {
	if (si->ref_count == 1) {
		TRACE("unloading '%s'", si->name);
		si->CallDestructors();

		if ((si->flags | FLAG_NEW_SOINFO) != 0) {
			si->get_children().for_each([&] (soinfo* child) {
				TRACE("%s needs to unload %s", si->name, child->name);
				soinfo_unload(child);
			});
		} else {
			for (ElfW(Dyn)* d = si->dynamic; d->d_tag != DT_NULL; ++d) {
				if (d->d_tag == DT_NEEDED) {
					const char* library_name = si->strtab + d->d_un.d_val;
					TRACE("%s needs to unload %s", si->name, library_name);
					soinfo* needed = find_library(library_name, RTLD_NOLOAD, NULL);
					if (needed != NULL) {
						soinfo_unload(needed);
					} else {
						// Not found: for example if symlink was deleted between dlopen and dlclose
						// Since we cannot really handle errors at this point - print and continue.
						PRINT("warning: couldn't find %s needed by %s on unload.", library_name, si->name);
					}
				}
			}
		}

		notify_gdb_of_unload(si);
		si->ref_count = 0;
		soinfo_free(si);
	} else {
		si->ref_count--;
		TRACE("not unloading '%s', decrementing ref_count to %zd", si->name, si->ref_count);
	}
}

void do_android_get_LD_LIBRARY_PATH(char* buffer, size_t buffer_size) {
	// Use basic string manipulation calls to avoid snprintf.
	// snprintf indirectly calls pthread_getspecific to get the size of a buffer.
	// When debug malloc is enabled, this call returns 0. This in turn causes
	// snprintf to do nothing, which causes libraries to fail to load.
	// See b/17302493 for further details.
	// Once the above bug is fixed, this code can be modified to use
	// snprintf again.
	size_t required_len = strlen(kDefaultLdPaths[0]) + strlen(kDefaultLdPaths[1]) + 2;
	if (buffer_size < required_len) {
		__libc_fatal("android_get_LD_LIBRARY_PATH failed, buffer too small: buffer len %zu, required len %zu",
								 buffer_size, required_len);
	}
	char* end = stpcpy(buffer, kDefaultLdPaths[0]);
	*end = ':';
	strcpy(end + 1, kDefaultLdPaths[1]);
}

void do_android_update_LD_LIBRARY_PATH(const char* ld_library_path) {
	if (!get_AT_SECURE()) {
		parse_LD_LIBRARY_PATH(ld_library_path);
	}
}

soinfo* do_dlopen(const char* name, int flags, const android_dlextinfo* extinfo) {//extinfo为空
	if ((flags & ~(RTLD_NOW|RTLD_LAZY|RTLD_LOCAL|RTLD_GLOBAL|RTLD_NOLOAD)) != 0) {
		DL_ERR("invalid flags to dlopen: %x", flags);
		return NULL;
	}
	if (extinfo != NULL && ((extinfo->flags & ~(ANDROID_DLEXT_VALID_FLAG_BITS)) != 0)) {
		DL_ERR("invalid extended flags to android_dlopen_ext: %" PRIx64, extinfo->flags);
		return NULL;
	}
	protect_data(PROT_READ | PROT_WRITE);
	soinfo* si = find_library(name, flags, extinfo);//加载链接name
	if (si != NULL) {
		//so文件加载到内存，并链接完成后，就开始调用so中的初始化函数
		si->CallConstructors();//初始化
	}
	protect_data(PROT_READ);
	return si;//返回值为soinfo对象的指针
}

void do_dlclose(soinfo* si) {
	protect_data(PROT_READ | PROT_WRITE);
	soinfo_unload(si);
	protect_data(PROT_READ);
}

#if defined(USE_RELA)
static int soinfo_relocate(soinfo* si, ElfW(Rela)* rela, unsigned count, soinfo* needed[]) {
	ElfW(Sym)* s;
	soinfo* lsi;

	for (size_t idx = 0; idx < count; ++idx, ++rela) {
		unsigned type = ELFW(R_TYPE)(rela->r_info);
		unsigned sym = ELFW(R_SYM)(rela->r_info);
		ElfW(Addr) reloc = static_cast<ElfW(Addr)>(rela->r_offset + si->load_bias);
		ElfW(Addr) sym_addr = 0;
		const char* sym_name = NULL;

		DEBUG("Processing '%s' relocation at index %zd", si->name, idx);
		if (type == 0) { // R_*_NONE
			continue;
		}
		if (sym != 0) {
			sym_name = reinterpret_cast<const char*>(si->strtab + si->symtab[sym].st_name);
			s = soinfo_do_lookup(si, sym_name, &lsi, needed);
			if (s == NULL) {
				// We only allow an undefined symbol if this is a weak reference...
				s = &si->symtab[sym];
				if (ELF_ST_BIND(s->st_info) != STB_WEAK) {
					DL_ERR("cannot locate symbol \"%s\" referenced by \"%s\"...", sym_name, si->name);
					return -1;
				}

				/* IHI0044C AAELF 4.5.1.1:

					 Libraries are not searched to resolve weak references.
					 It is not an error for a weak reference to remain unsatisfied.

					 During linking, the value of an undefined weak reference is:
					 - Zero if the relocation type is absolute
					 - The address of the place if the relocation is pc-relative
					 - The address of nominal base address if the relocation
						 type is base-relative.
				 */

				switch (type) {
#if defined(__aarch64__)
				case R_AARCH64_JUMP_SLOT:
				case R_AARCH64_GLOB_DAT:
				case R_AARCH64_ABS64:
				case R_AARCH64_ABS32:
				case R_AARCH64_ABS16:
				case R_AARCH64_RELATIVE:
					/*
					 * The sym_addr was initialized to be zero above, or the relocation
					 * code below does not care about value of sym_addr.
					 * No need to do anything.
					 */
					break;
#elif defined(__x86_64__)
				case R_X86_64_JUMP_SLOT:
				case R_X86_64_GLOB_DAT:
				case R_X86_64_32:
				case R_X86_64_64:
				case R_X86_64_RELATIVE:
					// No need to do anything.
					break;
				case R_X86_64_PC32:
					sym_addr = reloc;
					break;
#endif
				default:
					DL_ERR("unknown weak reloc type %d @ %p (%zu)", type, rela, idx);
					return -1;
				}
			} else {
				// We got a definition.
				sym_addr = static_cast<ElfW(Addr)>(s->st_value + lsi->load_bias);
			}
			count_relocation(kRelocSymbol);
		} else {
			s = NULL;
		}

		switch (type) {
#if defined(__aarch64__)
		case R_AARCH64_JUMP_SLOT:
				count_relocation(kRelocAbsolute);
				MARK(rela->r_offset);
				TRACE_TYPE(RELO, "RELO JMP_SLOT %16llx <- %16llx %s\n",
									 reloc, (sym_addr + rela->r_addend), sym_name);
				*reinterpret_cast<ElfW(Addr)*>(reloc) = (sym_addr + rela->r_addend);
				break;
		case R_AARCH64_GLOB_DAT:
				count_relocation(kRelocAbsolute);
				MARK(rela->r_offset);
				TRACE_TYPE(RELO, "RELO GLOB_DAT %16llx <- %16llx %s\n",
									 reloc, (sym_addr + rela->r_addend), sym_name);
				*reinterpret_cast<ElfW(Addr)*>(reloc) = (sym_addr + rela->r_addend);
				break;
		case R_AARCH64_ABS64:
				count_relocation(kRelocAbsolute);
				MARK(rela->r_offset);
				TRACE_TYPE(RELO, "RELO ABS64 %16llx <- %16llx %s\n",
									 reloc, (sym_addr + rela->r_addend), sym_name);
				*reinterpret_cast<ElfW(Addr)*>(reloc) += (sym_addr + rela->r_addend);
				break;
		case R_AARCH64_ABS32:
				count_relocation(kRelocAbsolute);
				MARK(rela->r_offset);
				TRACE_TYPE(RELO, "RELO ABS32 %16llx <- %16llx %s\n",
									 reloc, (sym_addr + rela->r_addend), sym_name);
				if ((static_cast<ElfW(Addr)>(INT32_MIN) <= (*reinterpret_cast<ElfW(Addr)*>(reloc) + (sym_addr + rela->r_addend))) &&
						((*reinterpret_cast<ElfW(Addr)*>(reloc) + (sym_addr + rela->r_addend)) <= static_cast<ElfW(Addr)>(UINT32_MAX))) {
						*reinterpret_cast<ElfW(Addr)*>(reloc) += (sym_addr + rela->r_addend);
				} else {
						DL_ERR("0x%016llx out of range 0x%016llx to 0x%016llx",
									 (*reinterpret_cast<ElfW(Addr)*>(reloc) + (sym_addr + rela->r_addend)),
									 static_cast<ElfW(Addr)>(INT32_MIN),
									 static_cast<ElfW(Addr)>(UINT32_MAX));
						return -1;
				}
				break;
		case R_AARCH64_ABS16:
				count_relocation(kRelocAbsolute);
				MARK(rela->r_offset);
				TRACE_TYPE(RELO, "RELO ABS16 %16llx <- %16llx %s\n",
									 reloc, (sym_addr + rela->r_addend), sym_name);
				if ((static_cast<ElfW(Addr)>(INT16_MIN) <= (*reinterpret_cast<ElfW(Addr)*>(reloc) + (sym_addr + rela->r_addend))) &&
						((*reinterpret_cast<ElfW(Addr)*>(reloc) + (sym_addr + rela->r_addend)) <= static_cast<ElfW(Addr)>(UINT16_MAX))) {
						*reinterpret_cast<ElfW(Addr)*>(reloc) += (sym_addr + rela->r_addend);
				} else {
						DL_ERR("0x%016llx out of range 0x%016llx to 0x%016llx",
									 (*reinterpret_cast<ElfW(Addr)*>(reloc) + (sym_addr + rela->r_addend)),
									 static_cast<ElfW(Addr)>(INT16_MIN),
									 static_cast<ElfW(Addr)>(UINT16_MAX));
						return -1;
				}
				break;
		case R_AARCH64_PREL64:
				count_relocation(kRelocRelative);
				MARK(rela->r_offset);
				TRACE_TYPE(RELO, "RELO REL64 %16llx <- %16llx - %16llx %s\n",
									 reloc, (sym_addr + rela->r_addend), rela->r_offset, sym_name);
				*reinterpret_cast<ElfW(Addr)*>(reloc) += (sym_addr + rela->r_addend) - rela->r_offset;
				break;
		case R_AARCH64_PREL32:
				count_relocation(kRelocRelative);
				MARK(rela->r_offset);
				TRACE_TYPE(RELO, "RELO REL32 %16llx <- %16llx - %16llx %s\n",
									 reloc, (sym_addr + rela->r_addend), rela->r_offset, sym_name);
				if ((static_cast<ElfW(Addr)>(INT32_MIN) <= (*reinterpret_cast<ElfW(Addr)*>(reloc) + ((sym_addr + rela->r_addend) - rela->r_offset))) &&
						((*reinterpret_cast<ElfW(Addr)*>(reloc) + ((sym_addr + rela->r_addend) - rela->r_offset)) <= static_cast<ElfW(Addr)>(UINT32_MAX))) {
						*reinterpret_cast<ElfW(Addr)*>(reloc) += ((sym_addr + rela->r_addend) - rela->r_offset);
				} else {
						DL_ERR("0x%016llx out of range 0x%016llx to 0x%016llx",
									 (*reinterpret_cast<ElfW(Addr)*>(reloc) + ((sym_addr + rela->r_addend) - rela->r_offset)),
									 static_cast<ElfW(Addr)>(INT32_MIN),
									 static_cast<ElfW(Addr)>(UINT32_MAX));
						return -1;
				}
				break;
		case R_AARCH64_PREL16:
				count_relocation(kRelocRelative);
				MARK(rela->r_offset);
				TRACE_TYPE(RELO, "RELO REL16 %16llx <- %16llx - %16llx %s\n",
									 reloc, (sym_addr + rela->r_addend), rela->r_offset, sym_name);
				if ((static_cast<ElfW(Addr)>(INT16_MIN) <= (*reinterpret_cast<ElfW(Addr)*>(reloc) + ((sym_addr + rela->r_addend) - rela->r_offset))) &&
						((*reinterpret_cast<ElfW(Addr)*>(reloc) + ((sym_addr + rela->r_addend) - rela->r_offset)) <= static_cast<ElfW(Addr)>(UINT16_MAX))) {
						*reinterpret_cast<ElfW(Addr)*>(reloc) += ((sym_addr + rela->r_addend) - rela->r_offset);
				} else {
						DL_ERR("0x%016llx out of range 0x%016llx to 0x%016llx",
									 (*reinterpret_cast<ElfW(Addr)*>(reloc) + ((sym_addr + rela->r_addend) - rela->r_offset)),
									 static_cast<ElfW(Addr)>(INT16_MIN),
									 static_cast<ElfW(Addr)>(UINT16_MAX));
						return -1;
				}
				break;

		case R_AARCH64_RELATIVE:
				count_relocation(kRelocRelative);
				MARK(rela->r_offset);
				if (sym) {
						DL_ERR("odd RELATIVE form...");
						return -1;
				}
				TRACE_TYPE(RELO, "RELO RELATIVE %16llx <- %16llx\n",
									 reloc, (si->base + rela->r_addend));
				*reinterpret_cast<ElfW(Addr)*>(reloc) = (si->base + rela->r_addend);
				break;

		case R_AARCH64_COPY:
				/*
				 * ET_EXEC is not supported so this should not happen.
				 *
				 * http://infocenter.arm.com/help/topic/com.arm.doc.ihi0044d/IHI0044D_aaelf.pdf
				 *
				 * Section 4.7.1.10 "Dynamic relocations"
				 * R_AARCH64_COPY may only appear in executable objects where e_type is
				 * set to ET_EXEC.
				 */
				DL_ERR("%s R_AARCH64_COPY relocations are not supported", si->name);
				return -1;
		case R_AARCH64_TLS_TPREL64:
				TRACE_TYPE(RELO, "RELO TLS_TPREL64 *** %16llx <- %16llx - %16llx\n",
									 reloc, (sym_addr + rela->r_addend), rela->r_offset);
				break;
		case R_AARCH64_TLS_DTPREL32:
				TRACE_TYPE(RELO, "RELO TLS_DTPREL32 *** %16llx <- %16llx - %16llx\n",
									 reloc, (sym_addr + rela->r_addend), rela->r_offset);
				break;
#elif defined(__x86_64__)
		case R_X86_64_JUMP_SLOT:
			count_relocation(kRelocAbsolute);
			MARK(rela->r_offset);
			TRACE_TYPE(RELO, "RELO JMP_SLOT %08zx <- %08zx %s", static_cast<size_t>(reloc),
								 static_cast<size_t>(sym_addr + rela->r_addend), sym_name);
			*reinterpret_cast<ElfW(Addr)*>(reloc) = sym_addr + rela->r_addend;
			break;
		case R_X86_64_GLOB_DAT:
			count_relocation(kRelocAbsolute);
			MARK(rela->r_offset);
			TRACE_TYPE(RELO, "RELO GLOB_DAT %08zx <- %08zx %s", static_cast<size_t>(reloc),
								 static_cast<size_t>(sym_addr + rela->r_addend), sym_name);
			*reinterpret_cast<ElfW(Addr)*>(reloc) = sym_addr + rela->r_addend;
			break;
		case R_X86_64_RELATIVE:
			count_relocation(kRelocRelative);
			MARK(rela->r_offset);
			if (sym) {
				DL_ERR("odd RELATIVE form...");
				return -1;
			}
			TRACE_TYPE(RELO, "RELO RELATIVE %08zx <- +%08zx", static_cast<size_t>(reloc),
								 static_cast<size_t>(si->base));
			*reinterpret_cast<ElfW(Addr)*>(reloc) = si->base + rela->r_addend;
			break;
		case R_X86_64_32:
			count_relocation(kRelocRelative);
			MARK(rela->r_offset);
			TRACE_TYPE(RELO, "RELO R_X86_64_32 %08zx <- +%08zx %s", static_cast<size_t>(reloc),
								 static_cast<size_t>(sym_addr), sym_name);
			*reinterpret_cast<ElfW(Addr)*>(reloc) = sym_addr + rela->r_addend;
			break;
		case R_X86_64_64:
			count_relocation(kRelocRelative);
			MARK(rela->r_offset);
			TRACE_TYPE(RELO, "RELO R_X86_64_64 %08zx <- +%08zx %s", static_cast<size_t>(reloc),
								 static_cast<size_t>(sym_addr), sym_name);
			*reinterpret_cast<ElfW(Addr)*>(reloc) = sym_addr + rela->r_addend;
			break;
		case R_X86_64_PC32:
			count_relocation(kRelocRelative);
			MARK(rela->r_offset);
			TRACE_TYPE(RELO, "RELO R_X86_64_PC32 %08zx <- +%08zx (%08zx - %08zx) %s",
								 static_cast<size_t>(reloc), static_cast<size_t>(sym_addr - reloc),
								 static_cast<size_t>(sym_addr), static_cast<size_t>(reloc), sym_name);
			*reinterpret_cast<ElfW(Addr)*>(reloc) = sym_addr + rela->r_addend - reloc;
			break;
#endif

		default:
			DL_ERR("unknown reloc type %d @ %p (%zu)", type, rela, idx);
			return -1;
		}
	}
	return 0;
}

#else // REL, not RELA.

static int soinfo_relocate(soinfo* si, ElfW(Rel)* rel, unsigned count, soinfo* needed[]) {
		ElfW(Sym)* s;
		soinfo* lsi;

		for (size_t idx = 0; idx < count; ++idx, ++rel) {
				unsigned type = ELFW(R_TYPE)(rel->r_info);
				// TODO: don't use unsigned for 'sym'. Use uint32_t or ElfW(Addr) instead.
				unsigned sym = ELFW(R_SYM)(rel->r_info);
				ElfW(Addr) reloc = static_cast<ElfW(Addr)>(rel->r_offset + si->load_bias);
				ElfW(Addr) sym_addr = 0;
				const char* sym_name = NULL;

				DEBUG("Processing '%s' relocation at index %zd", si->name, idx);
				if (type == 0) { // R_*_NONE
						continue;
				}
				if (sym != 0) {
						sym_name = reinterpret_cast<const char*>(si->strtab + si->symtab[sym].st_name);
						s = soinfo_do_lookup(si, sym_name, &lsi, needed);
						if (s == NULL) {
								// We only allow an undefined symbol if this is a weak reference...
								s = &si->symtab[sym];
								if (ELF_ST_BIND(s->st_info) != STB_WEAK) {
										DL_ERR("cannot locate symbol \"%s\" referenced by \"%s\"...", sym_name, si->name);
										return -1;
								}

								/* IHI0044C AAELF 4.5.1.1:

									 Libraries are not searched to resolve weak references.
									 It is not an error for a weak reference to remain
									 unsatisfied.

									 During linking, the value of an undefined weak reference is:
									 - Zero if the relocation type is absolute
									 - The address of the place if the relocation is pc-relative
									 - The address of nominal base address if the relocation
										 type is base-relative.
									*/

								switch (type) {
#if defined(__arm__)
								case R_ARM_JUMP_SLOT:
								case R_ARM_GLOB_DAT:
								case R_ARM_ABS32:
								case R_ARM_RELATIVE:    /* Don't care. */
										// sym_addr was initialized to be zero above or relocation
										// code below does not care about value of sym_addr.
										// No need to do anything.
										break;
#elif defined(__i386__)
								case R_386_JMP_SLOT:
								case R_386_GLOB_DAT:
								case R_386_32:
								case R_386_RELATIVE:    /* Don't care. */
										// sym_addr was initialized to be zero above or relocation
										// code below does not care about value of sym_addr.
										// No need to do anything.
										break;
								case R_386_PC32:
										sym_addr = reloc;
										break;
#endif

#if defined(__arm__)
								case R_ARM_COPY:
										// Fall through. Can't really copy if weak symbol is not found at run-time.
#endif
								default:
										DL_ERR("unknown weak reloc type %d @ %p (%zu)", type, rel, idx);
										return -1;
								}
						} else {
								// We got a definition.
								sym_addr = static_cast<ElfW(Addr)>(s->st_value + lsi->load_bias);
						}
						count_relocation(kRelocSymbol);
				} else {
						s = NULL;
				}

				switch (type) {
#if defined(__arm__)
				case R_ARM_JUMP_SLOT:
						count_relocation(kRelocAbsolute);
						MARK(rel->r_offset);
						TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s", reloc, sym_addr, sym_name);
						*reinterpret_cast<ElfW(Addr)*>(reloc) = sym_addr;
						break;
				case R_ARM_GLOB_DAT:
						count_relocation(kRelocAbsolute);
						MARK(rel->r_offset);
						TRACE_TYPE(RELO, "RELO GLOB_DAT %08x <- %08x %s", reloc, sym_addr, sym_name);
						*reinterpret_cast<ElfW(Addr)*>(reloc) = sym_addr;
						break;
				case R_ARM_ABS32:
						count_relocation(kRelocAbsolute);
						MARK(rel->r_offset);
						TRACE_TYPE(RELO, "RELO ABS %08x <- %08x %s", reloc, sym_addr, sym_name);
						*reinterpret_cast<ElfW(Addr)*>(reloc) += sym_addr;
						break;
				case R_ARM_REL32:
						count_relocation(kRelocRelative);
						MARK(rel->r_offset);
						TRACE_TYPE(RELO, "RELO REL32 %08x <- %08x - %08x %s",
											 reloc, sym_addr, rel->r_offset, sym_name);
						*reinterpret_cast<ElfW(Addr)*>(reloc) += sym_addr - rel->r_offset;
						break;
				case R_ARM_COPY:
						/*
						 * ET_EXEC is not supported so this should not happen.
						 *
						 * http://infocenter.arm.com/help/topic/com.arm.doc.ihi0044d/IHI0044D_aaelf.pdf
						 *
						 * Section 4.7.1.10 "Dynamic relocations"
						 * R_ARM_COPY may only appear in executable objects where e_type is
						 * set to ET_EXEC.
						 */
						DL_ERR("%s R_ARM_COPY relocations are not supported", si->name);
						return -1;
#elif defined(__i386__)
				case R_386_JMP_SLOT:
						count_relocation(kRelocAbsolute);
						MARK(rel->r_offset);
						TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s", reloc, sym_addr, sym_name);
						*reinterpret_cast<ElfW(Addr)*>(reloc) = sym_addr;
						break;
				case R_386_GLOB_DAT:
						count_relocation(kRelocAbsolute);
						MARK(rel->r_offset);
						TRACE_TYPE(RELO, "RELO GLOB_DAT %08x <- %08x %s", reloc, sym_addr, sym_name);
						*reinterpret_cast<ElfW(Addr)*>(reloc) = sym_addr;
						break;
				case R_386_32:
						count_relocation(kRelocRelative);
						MARK(rel->r_offset);
						TRACE_TYPE(RELO, "RELO R_386_32 %08x <- +%08x %s", reloc, sym_addr, sym_name);
						*reinterpret_cast<ElfW(Addr)*>(reloc) += sym_addr;
						break;
				case R_386_PC32:
						count_relocation(kRelocRelative);
						MARK(rel->r_offset);
						TRACE_TYPE(RELO, "RELO R_386_PC32 %08x <- +%08x (%08x - %08x) %s",
											 reloc, (sym_addr - reloc), sym_addr, reloc, sym_name);
						*reinterpret_cast<ElfW(Addr)*>(reloc) += (sym_addr - reloc);
						break;
#elif defined(__mips__)
				case R_MIPS_REL32:
#if defined(__LP64__)
						// MIPS Elf64_Rel entries contain compound relocations
						// We only handle the R_MIPS_NONE|R_MIPS_64|R_MIPS_REL32 case
						if (ELF64_R_TYPE2(rel->r_info) != R_MIPS_64 ||
								ELF64_R_TYPE3(rel->r_info) != R_MIPS_NONE) {
								DL_ERR("Unexpected compound relocation type:%d type2:%d type3:%d @ %p (%zu)",
											 type, (unsigned)ELF64_R_TYPE2(rel->r_info),
											 (unsigned)ELF64_R_TYPE3(rel->r_info), rel, idx);
								return -1;
						}
#endif
						count_relocation(kRelocAbsolute);
						MARK(rel->r_offset);
						TRACE_TYPE(RELO, "RELO REL32 %08zx <- %08zx %s", static_cast<size_t>(reloc),
											 static_cast<size_t>(sym_addr), sym_name ? sym_name : "*SECTIONHDR*");
						if (s) {
								*reinterpret_cast<ElfW(Addr)*>(reloc) += sym_addr;
						} else {
								*reinterpret_cast<ElfW(Addr)*>(reloc) += si->base;
						}
						break;
#endif

#if defined(__arm__)
				case R_ARM_RELATIVE:
#elif defined(__i386__)
				case R_386_RELATIVE:
#endif
						count_relocation(kRelocRelative);
						MARK(rel->r_offset);
						if (sym) {
								DL_ERR("odd RELATIVE form...");
								return -1;
						}
						TRACE_TYPE(RELO, "RELO RELATIVE %p <- +%p",
											 reinterpret_cast<void*>(reloc), reinterpret_cast<void*>(si->base));
						*reinterpret_cast<ElfW(Addr)*>(reloc) += si->base;
						break;

				default:
						DL_ERR("unknown reloc type %d @ %p (%zu)", type, rel, idx);
						return -1;
				}
		}
		return 0;
}
#endif

#if defined(__mips__)
static bool mips_relocate_got(soinfo* si, soinfo* needed[]) {
		ElfW(Addr)** got = si->plt_got;
		if (got == NULL) {
				return true;
		}
		unsigned local_gotno = si->mips_local_gotno;
		unsigned gotsym = si->mips_gotsym;
		unsigned symtabno = si->mips_symtabno;
		ElfW(Sym)* symtab = si->symtab;

		// got[0] is the address of the lazy resolver function.
		// got[1] may be used for a GNU extension.
		// Set it to a recognizable address in case someone calls it (should be _rtld_bind_start).
		// FIXME: maybe this should be in a separate routine?
		if ((si->flags & FLAG_LINKER) == 0) {
				size_t g = 0;
				got[g++] = reinterpret_cast<ElfW(Addr)*>(0xdeadbeef);
				if (reinterpret_cast<intptr_t>(got[g]) < 0) {
						got[g++] = reinterpret_cast<ElfW(Addr)*>(0xdeadfeed);
				}
				// Relocate the local GOT entries.
				for (; g < local_gotno; g++) {
						got[g] = reinterpret_cast<ElfW(Addr)*>(reinterpret_cast<uintptr_t>(got[g]) + si->load_bias);
				}
		}

		// Now for the global GOT entries...
		ElfW(Sym)* sym = symtab + gotsym;
		got = si->plt_got + local_gotno;
		for (size_t g = gotsym; g < symtabno; g++, sym++, got++) {
				// This is an undefined reference... try to locate it.
				const char* sym_name = si->strtab + sym->st_name;
				soinfo* lsi;
				ElfW(Sym)* s = soinfo_do_lookup(si, sym_name, &lsi, needed);
				if (s == NULL) {
						// We only allow an undefined symbol if this is a weak reference.
						s = &symtab[g];
						if (ELF_ST_BIND(s->st_info) != STB_WEAK) {
								DL_ERR("cannot locate \"%s\"...", sym_name);
								return false;
						}
						*got = 0;
				} else {
						// FIXME: is this sufficient?
						// For reference see NetBSD link loader
						// http://cvsweb.netbsd.org/bsdweb.cgi/src/libexec/ld.elf_so/arch/mips/mips_reloc.c?rev=1.53&content-type=text/x-cvsweb-markup
						*got = reinterpret_cast<ElfW(Addr)*>(lsi->load_bias + s->st_value);
				}
		}
		return true;
}
#endif

void soinfo::CallArray(const char* array_name __unused, linker_function_t* functions, size_t count, bool reverse) {
	if (functions == NULL) {
		return;
	}

	TRACE("[ Calling %s (size %zd) @ %p for '%s' ]", array_name, count, functions, name);

	int begin = reverse ? (count - 1) : 0;
	int end = reverse ? -1 : count;
	int step = reverse ? -1 : 1;

	for (int i = begin; i != end; i += step) {
		TRACE("[ %s[%d] == %p ]", array_name, i, functions[i]);
		CallFunction("function", functions[i]);
	}

	TRACE("[ Done calling %s for '%s' ]", array_name, name);
}

void soinfo::CallFunction(const char* function_name __unused, linker_function_t function) {
	if (function == NULL || reinterpret_cast<uintptr_t>(function) == static_cast<uintptr_t>(-1)) {
		return;
	}

	TRACE("[ Calling %s @ %p for '%s' ]", function_name, function, name);
	function();
	TRACE("[ Done calling %s @ %p for '%s' ]", function_name, function, name);

	// The function may have called dlopen(3) or dlclose(3), so we need to ensure our data structures
	// are still writable. This happens with our debug malloc (see http://b/7941716).
	protect_data(PROT_READ | PROT_WRITE);
}

void soinfo::CallPreInitConstructors() {
	// DT_PREINIT_ARRAY functions are called before any other constructors for executables,
	// but ignored in a shared library.
	CallArray("DT_PREINIT_ARRAY", preinit_array, preinit_array_count, false);
}

void soinfo::CallConstructors() {
	if (constructors_called) {
		return;
	}

	// We set constructors_called before actually calling the constructors, otherwise it doesn't
	// protect against recursive constructor calls. One simple example of constructor recursion
	// is the libc debug malloc, which is implemented in libc_malloc_debug_leak.so:
	// 1. The program depends on libc, so libc's constructor is called here.
	// 2. The libc constructor calls dlopen() to load libc_malloc_debug_leak.so.
	// 3. dlopen() calls the constructors on the newly created
	//    soinfo for libc_malloc_debug_leak.so.
	// 4. The debug .so depends on libc, so CallConstructors is
	//    called again with the libc soinfo. If it doesn't trigger the early-
	//    out above, the libc constructor will be called again (recursively!).
	constructors_called = true;

	if ((flags & FLAG_EXE) == 0 && preinit_array != NULL) {
		// The GNU dynamic linker silently ignores these, but we warn the developer.
		PRINT("\"%s\": ignoring %zd-entry DT_PREINIT_ARRAY in shared library!",
					name, preinit_array_count);
	}

	get_children().for_each([] (soinfo* si) {
		si->CallConstructors();
	});

	TRACE("\"%s\": calling constructors", name);

	// DT_INIT should be called before DT_INIT_ARRAY if both are present.
	//通常加壳逻辑就放在 init_func 或 init_array 中，它们先于 jni_onLoad 执行
	CallFunction("DT_INIT", init_func);//调用 init_func 函数
	CallArray("DT_INIT_ARRAY", init_array, init_array_count, false);//调用init_array数组中的函数
}

void soinfo::CallDestructors() {
	TRACE("\"%s\": calling destructors", name);

	// DT_FINI_ARRAY must be parsed in reverse order.
	CallArray("DT_FINI_ARRAY", fini_array, fini_array_count, true);

	// DT_FINI should be called after DT_FINI_ARRAY if both are present.
	CallFunction("DT_FINI", fini_func);

	// This is needed on second call to dlopen
	// after library has been unloaded with RTLD_NODELETE
	constructors_called = false;
}

void soinfo::add_child(soinfo* child) {
	if ((this->flags & FLAG_NEW_SOINFO) == 0) {
		return;
	}

	this->children.push_front(child);
	child->parents.push_front(this);
}

void soinfo::remove_all_links() {
	if ((this->flags & FLAG_NEW_SOINFO) == 0) {
		return;
	}

	// 1. Untie connected soinfos from 'this'.
	children.for_each([&] (soinfo* child) {
		child->parents.remove_if([&] (const soinfo* parent) {
			return parent == this;
		});
	});

	parents.for_each([&] (soinfo* parent) {
		parent->children.for_each([&] (const soinfo* child) {
			return child == this;
		});
	});

	// 2. Once everything untied - clear local lists.
	parents.clear();
	children.clear();
}

void soinfo::set_st_dev(dev_t dev) {
	if ((this->flags & FLAG_NEW_SOINFO) == 0) {
		return;
	}

	st_dev = dev;
}

void soinfo::set_st_ino(ino_t ino) {
	if ((this->flags & FLAG_NEW_SOINFO) == 0) {
		return;
	}

	st_ino = ino;
}

dev_t soinfo::get_st_dev() {
	if ((this->flags & FLAG_NEW_SOINFO) == 0) {
		return 0;
	}

	return st_dev;
};

ino_t soinfo::get_st_ino() {
	if ((this->flags & FLAG_NEW_SOINFO) == 0) {
		return 0;
	}

	return st_ino;
}

// This is a return on get_children() in case
// 'this->flags' does not have FLAG_NEW_SOINFO set.
static soinfo::soinfo_list_t g_empty_list;

soinfo::soinfo_list_t& soinfo::get_children() {
	if ((this->flags & FLAG_NEW_SOINFO) == 0) {
		return g_empty_list;
	}

	return this->children;
}

/* Force any of the closed stdin, stdout and stderr to be associated with
	 /dev/null. */
static int nullify_closed_stdio() {
		int dev_null, i, status;
		int return_value = 0;

		dev_null = TEMP_FAILURE_RETRY(open("/dev/null", O_RDWR));
		if (dev_null < 0) {
				DL_ERR("cannot open /dev/null: %s", strerror(errno));
				return -1;
		}
		TRACE("[ Opened /dev/null file-descriptor=%d]", dev_null);

		/* If any of the stdio file descriptors is valid and not associated
			 with /dev/null, dup /dev/null to it.  */
		for (i = 0; i < 3; i++) {
				/* If it is /dev/null already, we are done. */
				if (i == dev_null) {
						continue;
				}

				TRACE("[ Nullifying stdio file descriptor %d]", i);
				status = TEMP_FAILURE_RETRY(fcntl(i, F_GETFL));

				/* If file is opened, we are good. */
				if (status != -1) {
						continue;
				}

				/* The only error we allow is that the file descriptor does not
					 exist, in which case we dup /dev/null to it. */
				if (errno != EBADF) {
						DL_ERR("fcntl failed: %s", strerror(errno));
						return_value = -1;
						continue;
				}

				/* Try dupping /dev/null to this stdio file descriptor and
					 repeat if there is a signal.  Note that any errors in closing
					 the stdio descriptor are lost.  */
				status = TEMP_FAILURE_RETRY(dup2(dev_null, i));
				if (status < 0) {
						DL_ERR("dup2 failed: %s", strerror(errno));
						return_value = -1;
						continue;
				}
		}

		/* If /dev/null is not one of the stdio file descriptors, close it. */
		if (dev_null > 2) {
				TRACE("[ Closing /dev/null file-descriptor=%d]", dev_null);
				status = TEMP_FAILURE_RETRY(close(dev_null));
				if (status == -1) {
						DL_ERR("close failed: %s", strerror(errno));
						return_value = -1;
				}
		}

		return return_value;
}

static bool soinfo_link_image(soinfo* si, const android_dlextinfo* extinfo) {
		/* "base" might wrap around UINT32_MAX. */
		ElfW(Addr) base = si->load_bias;
		const ElfW(Phdr)* phdr = si->phdr;
		int phnum = si->phnum;
		bool relocating_linker = (si->flags & FLAG_LINKER) != 0;

		/* We can't debug anything until the linker is relocated */
		if (!relocating_linker) {
				INFO("[ linking %s ]", si->name);
				DEBUG("si->base = %p si->flags = 0x%08x", reinterpret_cast<void*>(si->base), si->flags);
		}

		/* Extract dynamic section */
		size_t dynamic_count;
		ElfW(Word) dynamic_flags;
		phdr_table_get_dynamic_section(phdr, phnum, base, &si->dynamic,
																	 &dynamic_count, &dynamic_flags);
		if (si->dynamic == NULL) {
				if (!relocating_linker) {
						DL_ERR("missing PT_DYNAMIC in \"%s\"", si->name);
				}
				return false;
		} else {
				if (!relocating_linker) {
						DEBUG("dynamic = %p", si->dynamic);
				}
		}

#if defined(__arm__)
		(void) phdr_table_get_arm_exidx(phdr, phnum, base,
																		&si->ARM_exidx, &si->ARM_exidx_count);
#endif

		// Extract useful information from dynamic section.
		uint32_t needed_count = 0;
		for (ElfW(Dyn)* d = si->dynamic; d->d_tag != DT_NULL; ++d) {
				DEBUG("d = %p, d[0](tag) = %p d[1](val) = %p",
							d, reinterpret_cast<void*>(d->d_tag), reinterpret_cast<void*>(d->d_un.d_val));
				switch (d->d_tag) {
				case DT_HASH:
						si->nbucket = reinterpret_cast<uint32_t*>(base + d->d_un.d_ptr)[0];
						si->nchain = reinterpret_cast<uint32_t*>(base + d->d_un.d_ptr)[1];
						si->bucket = reinterpret_cast<uint32_t*>(base + d->d_un.d_ptr + 8);
						si->chain = reinterpret_cast<uint32_t*>(base + d->d_un.d_ptr + 8 + si->nbucket * 4);
						break;
				case DT_STRTAB:
						si->strtab = reinterpret_cast<const char*>(base + d->d_un.d_ptr);
						break;
				case DT_SYMTAB:
						si->symtab = reinterpret_cast<ElfW(Sym)*>(base + d->d_un.d_ptr);
						break;
#if !defined(__LP64__)
				case DT_PLTREL:
						if (d->d_un.d_val != DT_REL) {
								DL_ERR("unsupported DT_RELA in \"%s\"", si->name);
								return false;
						}
						break;
#endif
				case DT_JMPREL:
#if defined(USE_RELA)
						si->plt_rela = reinterpret_cast<ElfW(Rela)*>(base + d->d_un.d_ptr);
#else
						si->plt_rel = reinterpret_cast<ElfW(Rel)*>(base + d->d_un.d_ptr);
#endif
						break;
				case DT_PLTRELSZ:
#if defined(USE_RELA)
						si->plt_rela_count = d->d_un.d_val / sizeof(ElfW(Rela));
#else
						si->plt_rel_count = d->d_un.d_val / sizeof(ElfW(Rel));
#endif
						break;
#if defined(__mips__)
				case DT_PLTGOT:
						// Used by mips and mips64.
						si->plt_got = reinterpret_cast<ElfW(Addr)**>(base + d->d_un.d_ptr);
						break;
#endif
				case DT_DEBUG:
						// Set the DT_DEBUG entry to the address of _r_debug for GDB
						// if the dynamic table is writable
// FIXME: not working currently for N64
// The flags for the LOAD and DYNAMIC program headers do not agree.
// The LOAD section containng the dynamic table has been mapped as
// read-only, but the DYNAMIC header claims it is writable.
#if !(defined(__mips__) && defined(__LP64__))
						if ((dynamic_flags & PF_W) != 0) {
								d->d_un.d_val = reinterpret_cast<uintptr_t>(&_r_debug);
						}
						break;
#endif
#if defined(USE_RELA)
				 case DT_RELA:
						si->rela = reinterpret_cast<ElfW(Rela)*>(base + d->d_un.d_ptr);
						break;
				 case DT_RELASZ:
						si->rela_count = d->d_un.d_val / sizeof(ElfW(Rela));
						break;
				case DT_REL:
						DL_ERR("unsupported DT_REL in \"%s\"", si->name);
						return false;
				case DT_RELSZ:
						DL_ERR("unsupported DT_RELSZ in \"%s\"", si->name);
						return false;
#else
				case DT_REL:
						si->rel = reinterpret_cast<ElfW(Rel)*>(base + d->d_un.d_ptr);
						break;
				case DT_RELSZ:
						si->rel_count = d->d_un.d_val / sizeof(ElfW(Rel));
						break;
				 case DT_RELA:
						DL_ERR("unsupported DT_RELA in \"%s\"", si->name);
						return false;
#endif
				case DT_INIT:
						si->init_func = reinterpret_cast<linker_function_t>(base + d->d_un.d_ptr);
						DEBUG("%s constructors (DT_INIT) found at %p", si->name, si->init_func);
						break;
				case DT_FINI:
						si->fini_func = reinterpret_cast<linker_function_t>(base + d->d_un.d_ptr);
						DEBUG("%s destructors (DT_FINI) found at %p", si->name, si->fini_func);
						break;
				case DT_INIT_ARRAY:
						si->init_array = reinterpret_cast<linker_function_t*>(base + d->d_un.d_ptr);
						DEBUG("%s constructors (DT_INIT_ARRAY) found at %p", si->name, si->init_array);
						break;
				case DT_INIT_ARRAYSZ:
						si->init_array_count = ((unsigned)d->d_un.d_val) / sizeof(ElfW(Addr));
						break;
				case DT_FINI_ARRAY:
						si->fini_array = reinterpret_cast<linker_function_t*>(base + d->d_un.d_ptr);
						DEBUG("%s destructors (DT_FINI_ARRAY) found at %p", si->name, si->fini_array);
						break;
				case DT_FINI_ARRAYSZ:
						si->fini_array_count = ((unsigned)d->d_un.d_val) / sizeof(ElfW(Addr));
						break;
				case DT_PREINIT_ARRAY:
						si->preinit_array = reinterpret_cast<linker_function_t*>(base + d->d_un.d_ptr);
						DEBUG("%s constructors (DT_PREINIT_ARRAY) found at %p", si->name, si->preinit_array);
						break;
				case DT_PREINIT_ARRAYSZ:
						si->preinit_array_count = ((unsigned)d->d_un.d_val) / sizeof(ElfW(Addr));
						break;
				case DT_TEXTREL:
#if defined(__LP64__)
						DL_ERR("text relocations (DT_TEXTREL) found in 64-bit ELF file \"%s\"", si->name);
						return false;
#else
						si->has_text_relocations = true;
						break;
#endif
				case DT_SYMBOLIC:
						si->has_DT_SYMBOLIC = true;
						break;
				case DT_NEEDED:
						++needed_count;
						break;
				case DT_FLAGS:
						if (d->d_un.d_val & DF_TEXTREL) {
#if defined(__LP64__)
								DL_ERR("text relocations (DF_TEXTREL) found in 64-bit ELF file \"%s\"", si->name);
								return false;
#else
								si->has_text_relocations = true;
#endif
						}
						if (d->d_un.d_val & DF_SYMBOLIC) {
								si->has_DT_SYMBOLIC = true;
						}
						break;
#if defined(__mips__)
				case DT_STRSZ:
				case DT_SYMENT:
				case DT_RELENT:
						 break;
				case DT_MIPS_RLD_MAP:
						// Set the DT_MIPS_RLD_MAP entry to the address of _r_debug for GDB.
						{
							r_debug** dp = reinterpret_cast<r_debug**>(base + d->d_un.d_ptr);
							*dp = &_r_debug;
						}
						break;
				case DT_MIPS_RLD_VERSION:
				case DT_MIPS_FLAGS:
				case DT_MIPS_BASE_ADDRESS:
				case DT_MIPS_UNREFEXTNO:
						break;

				case DT_MIPS_SYMTABNO:
						si->mips_symtabno = d->d_un.d_val;
						break;

				case DT_MIPS_LOCAL_GOTNO:
						si->mips_local_gotno = d->d_un.d_val;
						break;

				case DT_MIPS_GOTSYM:
						si->mips_gotsym = d->d_un.d_val;
						break;
#endif

				default:
						DEBUG("Unused DT entry: type %p arg %p",
									reinterpret_cast<void*>(d->d_tag), reinterpret_cast<void*>(d->d_un.d_val));
						break;
				}
		}

		DEBUG("si->base = %p, si->strtab = %p, si->symtab = %p",
					reinterpret_cast<void*>(si->base), si->strtab, si->symtab);

		// Sanity checks.
		if (relocating_linker && needed_count != 0) {
				DL_ERR("linker cannot have DT_NEEDED dependencies on other libraries");
				return false;
		}
		if (si->nbucket == 0) {
				DL_ERR("empty/missing DT_HASH in \"%s\" (built with --hash-style=gnu?)", si->name);
				return false;
		}
		if (si->strtab == 0) {
				DL_ERR("empty/missing DT_STRTAB in \"%s\"", si->name);
				return false;
		}
		if (si->symtab == 0) {
				DL_ERR("empty/missing DT_SYMTAB in \"%s\"", si->name);
				return false;
		}

		// If this is the main executable, then load all of the libraries from LD_PRELOAD now.
		if (si->flags & FLAG_EXE) {
				memset(g_ld_preloads, 0, sizeof(g_ld_preloads));
				size_t preload_count = 0;
				for (size_t i = 0; g_ld_preload_names[i] != NULL; i++) {
						soinfo* lsi = find_library(g_ld_preload_names[i], 0, NULL);
						if (lsi != NULL) {
								g_ld_preloads[preload_count++] = lsi;
						} else {
								// As with glibc, failure to load an LD_PRELOAD library is just a warning.
								DL_WARN("could not load library \"%s\" from LD_PRELOAD for \"%s\"; caused by %s",
												g_ld_preload_names[i], si->name, linker_get_error_buffer());
						}
				}
		}

		soinfo** needed = reinterpret_cast<soinfo**>(alloca((1 + needed_count) * sizeof(soinfo*)));
		soinfo** pneeded = needed;

		for (ElfW(Dyn)* d = si->dynamic; d->d_tag != DT_NULL; ++d) {
				if (d->d_tag == DT_NEEDED) {
						const char* library_name = si->strtab + d->d_un.d_val;
						DEBUG("%s needs %s", si->name, library_name);
						soinfo* lsi = find_library(library_name, 0, NULL);
						if (lsi == NULL) {
								strlcpy(tmp_err_buf, linker_get_error_buffer(), sizeof(tmp_err_buf));
								DL_ERR("could not load library \"%s\" needed by \"%s\"; caused by %s",
											 library_name, si->name, tmp_err_buf);
								return false;
						}

						si->add_child(lsi);
						*pneeded++ = lsi;
				}
		}
		*pneeded = NULL;

#if !defined(__LP64__)
		if (si->has_text_relocations) {
				// Make segments writable to allow text relocations to work properly. We will later call
				// phdr_table_protect_segments() after all of them are applied and all constructors are run.
				DL_WARN("%s has text relocations. This is wasting memory and prevents "
								"security hardening. Please fix.", si->name);
				if (phdr_table_unprotect_segments(si->phdr, si->phnum, si->load_bias) < 0) {
						DL_ERR("can't unprotect loadable segments for \"%s\": %s",
									 si->name, strerror(errno));
						return false;
				}
		}
#endif

#if defined(USE_RELA)
		if (si->plt_rela != NULL) {
				DEBUG("[ relocating %s plt ]\n", si->name);
				if (soinfo_relocate(si, si->plt_rela, si->plt_rela_count, needed)) {
						return false;
				}
		}
		if (si->rela != NULL) {
				DEBUG("[ relocating %s ]\n", si->name);
				if (soinfo_relocate(si, si->rela, si->rela_count, needed)) {
						return false;
				}
		}
#else
		if (si->plt_rel != NULL) {
				DEBUG("[ relocating %s plt ]", si->name);
				if (soinfo_relocate(si, si->plt_rel, si->plt_rel_count, needed)) {
						return false;
				}
		}
		if (si->rel != NULL) {
				DEBUG("[ relocating %s ]", si->name);
				if (soinfo_relocate(si, si->rel, si->rel_count, needed)) {
						return false;
				}
		}
#endif

#if defined(__mips__)
		if (!mips_relocate_got(si, needed)) {
				return false;
		}
#endif

		si->flags |= FLAG_LINKED;
		DEBUG("[ finished linking %s ]", si->name);

#if !defined(__LP64__)
		if (si->has_text_relocations) {
				// All relocations are done, we can protect our segments back to read-only.
				if (phdr_table_protect_segments(si->phdr, si->phnum, si->load_bias) < 0) {
						DL_ERR("can't protect segments for \"%s\": %s",
									 si->name, strerror(errno));
						return false;
				}
		}
#endif

		/* We can also turn on GNU RELRO protection */
		if (phdr_table_protect_gnu_relro(si->phdr, si->phnum, si->load_bias) < 0) {
				DL_ERR("can't enable GNU RELRO protection for \"%s\": %s",
							 si->name, strerror(errno));
				return false;
		}

		/* Handle serializing/sharing the RELRO segment */
		if (extinfo && (extinfo->flags & ANDROID_DLEXT_WRITE_RELRO)) {
			if (phdr_table_serialize_gnu_relro(si->phdr, si->phnum, si->load_bias,
																				 extinfo->relro_fd) < 0) {
				DL_ERR("failed serializing GNU RELRO section for \"%s\": %s",
							 si->name, strerror(errno));
				return false;
			}
		} else if (extinfo && (extinfo->flags & ANDROID_DLEXT_USE_RELRO)) {
			if (phdr_table_map_gnu_relro(si->phdr, si->phnum, si->load_bias,
																	 extinfo->relro_fd) < 0) {
				DL_ERR("failed mapping GNU RELRO section for \"%s\": %s",
							 si->name, strerror(errno));
				return false;
			}
		}

		notify_gdb_of_load(si);
		return true;
}

/*
 * This function add vdso to internal dso list.
 * It helps to stack unwinding through signal handlers.
 * Also, it makes bionic more like glibc.
 */
static void add_vdso(KernelArgumentBlock& args __unused) {
#if defined(AT_SYSINFO_EHDR)
	ElfW(Ehdr)* ehdr_vdso = reinterpret_cast<ElfW(Ehdr)*>(args.getauxval(AT_SYSINFO_EHDR));
	if (ehdr_vdso == NULL) {
		return;
	}

	soinfo* si = soinfo_alloc("[vdso]", NULL);

	si->phdr = reinterpret_cast<ElfW(Phdr)*>(reinterpret_cast<char*>(ehdr_vdso) + ehdr_vdso->e_phoff);
	si->phnum = ehdr_vdso->e_phnum;
	si->base = reinterpret_cast<ElfW(Addr)>(ehdr_vdso);
	si->size = phdr_table_get_load_size(si->phdr, si->phnum);
	si->load_bias = get_elf_exec_load_bias(ehdr_vdso);

	soinfo_link_image(si, NULL);
#endif
}

/*
 * This is linker soinfo for GDB. See details below.
 */
static soinfo linker_soinfo_for_gdb;

/* gdb expects the linker to be in the debug shared object list.
 * Without this, gdb has trouble locating the linker's ".text"
 * and ".plt" sections. Gdb could also potentially use this to
 * relocate the offset of our exported 'rtld_db_dlactivity' symbol.
 * Don't use soinfo_alloc(), because the linker shouldn't
 * be on the soinfo list.
 */
static void init_linker_info_for_gdb(ElfW(Addr) linker_base) {
#if defined(__LP64__)
	strlcpy(linker_soinfo_for_gdb.name, "/system/bin/linker64", sizeof(linker_soinfo_for_gdb.name));
#else
	strlcpy(linker_soinfo_for_gdb.name, "/system/bin/linker", sizeof(linker_soinfo_for_gdb.name));
#endif
	linker_soinfo_for_gdb.flags = FLAG_NEW_SOINFO;
	linker_soinfo_for_gdb.base = linker_base;

	/*
	 * Set the dynamic field in the link map otherwise gdb will complain with
	 * the following:
	 *   warning: .dynamic section for "/system/bin/linker" is not at the
	 *   expected address (wrong library or version mismatch?)
	 */
	ElfW(Ehdr)* elf_hdr = reinterpret_cast<ElfW(Ehdr)*>(linker_base);
	ElfW(Phdr)* phdr = reinterpret_cast<ElfW(Phdr)*>(linker_base + elf_hdr->e_phoff);
	phdr_table_get_dynamic_section(phdr, elf_hdr->e_phnum, linker_base,
																 &linker_soinfo_for_gdb.dynamic, NULL, NULL);
	insert_soinfo_into_debug_map(&linker_soinfo_for_gdb);
}

/*
 * This code is called after the linker has linked itself and
 * fixed it's own GOT. It is safe to make references to externs
 * and other non-local data at this point.
 */
static ElfW(Addr) __linker_init_post_relocation(KernelArgumentBlock& args, ElfW(Addr) linker_base) {
		/* NOTE: we store the args pointer on a special location
		 *       of the temporary TLS area in order to pass it to
		 *       the C Library's runtime initializer.
		 *
		 *       The initializer must clear the slot and reset the TLS
		 *       to point to a different location to ensure that no other
		 *       shared library constructor can access it.
		 */
	__libc_init_tls(args);

#if TIMING
		struct timeval t0, t1;
		gettimeofday(&t0, 0);
#endif

		// Initialize environment functions, and get to the ELF aux vectors table.
		linker_env_init(args);

		// If this is a setuid/setgid program, close the security hole described in
		// ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-02:23.stdio.asc
		if (get_AT_SECURE()) {
				nullify_closed_stdio();
		}

		debuggerd_init();

		// Get a few environment variables.
		const char* LD_DEBUG = linker_env_get("LD_DEBUG");
		if (LD_DEBUG != NULL) {
			g_ld_debug_verbosity = atoi(LD_DEBUG);
		}

		// Normally, these are cleaned by linker_env_init, but the test
		// doesn't cost us anything.
		const char* ldpath_env = NULL;
		const char* ldpreload_env = NULL;
		if (!get_AT_SECURE()) {
			ldpath_env = linker_env_get("LD_LIBRARY_PATH");
			ldpreload_env = linker_env_get("LD_PRELOAD");
		}

		INFO("[ android linker & debugger ]");

		soinfo* si = soinfo_alloc(args.argv[0], NULL);
		if (si == NULL) {
				exit(EXIT_FAILURE);
		}

		/* bootstrap the link map, the main exe always needs to be first */
		si->flags |= FLAG_EXE;
		link_map* map = &(si->link_map_head);

		map->l_addr = 0;
		map->l_name = args.argv[0];
		map->l_prev = NULL;
		map->l_next = NULL;

		_r_debug.r_map = map;
		r_debug_tail = map;

		init_linker_info_for_gdb(linker_base);

		// Extract information passed from the kernel.
		si->phdr = reinterpret_cast<ElfW(Phdr)*>(args.getauxval(AT_PHDR));
		si->phnum = args.getauxval(AT_PHNUM);
		si->entry = args.getauxval(AT_ENTRY);

		/* Compute the value of si->base. We can't rely on the fact that
		 * the first entry is the PHDR because this will not be true
		 * for certain executables (e.g. some in the NDK unit test suite)
		 */
		si->base = 0;
		si->size = phdr_table_get_load_size(si->phdr, si->phnum);
		si->load_bias = 0;
		for (size_t i = 0; i < si->phnum; ++i) {
			if (si->phdr[i].p_type == PT_PHDR) {
				si->load_bias = reinterpret_cast<ElfW(Addr)>(si->phdr) - si->phdr[i].p_vaddr;
				si->base = reinterpret_cast<ElfW(Addr)>(si->phdr) - si->phdr[i].p_offset;
				break;
			}
		}
		si->dynamic = NULL;
		si->ref_count = 1;

		ElfW(Ehdr)* elf_hdr = reinterpret_cast<ElfW(Ehdr)*>(si->base);
		if (elf_hdr->e_type != ET_DYN) {
				__libc_format_fd(2, "error: only position independent executables (PIE) are supported.\n");
				exit(EXIT_FAILURE);
		}

		// Use LD_LIBRARY_PATH and LD_PRELOAD (but only if we aren't setuid/setgid).
		parse_LD_LIBRARY_PATH(ldpath_env);
		parse_LD_PRELOAD(ldpreload_env);

		somain = si;

		if (!soinfo_link_image(si, NULL)) {
				__libc_format_fd(2, "CANNOT LINK EXECUTABLE: %s\n", linker_get_error_buffer());
				exit(EXIT_FAILURE);
		}

		add_vdso(args);

		si->CallPreInitConstructors();

		for (size_t i = 0; g_ld_preloads[i] != NULL; ++i) {
				g_ld_preloads[i]->CallConstructors();
		}

		/* After the link_image, the si->load_bias is initialized.
		 * For so lib, the map->l_addr will be updated in notify_gdb_of_load.
		 * We need to update this value for so exe here. So Unwind_Backtrace
		 * for some arch like x86 could work correctly within so exe.
		 */
		map->l_addr = si->load_bias;
		si->CallConstructors();

#if TIMING
		gettimeofday(&t1, NULL);
		PRINT("LINKER TIME: %s: %d microseconds", args.argv[0], (int) (
							 (((long long)t1.tv_sec * 1000000LL) + (long long)t1.tv_usec) -
							 (((long long)t0.tv_sec * 1000000LL) + (long long)t0.tv_usec)));
#endif
#if STATS
		PRINT("RELO STATS: %s: %d abs, %d rel, %d copy, %d symbol", args.argv[0],
					 linker_stats.count[kRelocAbsolute],
					 linker_stats.count[kRelocRelative],
					 linker_stats.count[kRelocCopy],
					 linker_stats.count[kRelocSymbol]);
#endif
#if COUNT_PAGES
		{
				unsigned n;
				unsigned i;
				unsigned count = 0;
				for (n = 0; n < 4096; n++) {
						if (bitmask[n]) {
								unsigned x = bitmask[n];
#if defined(__LP64__)
								for (i = 0; i < 32; i++) {
#else
								for (i = 0; i < 8; i++) {
#endif
										if (x & 1) {
												count++;
										}
										x >>= 1;
								}
						}
				}
				PRINT("PAGES MODIFIED: %s: %d (%dKB)", args.argv[0], count, count * 4);
		}
#endif

#if TIMING || STATS || COUNT_PAGES
		fflush(stdout);
#endif

		TRACE("[ Ready to execute '%s' @ %p ]", si->name, reinterpret_cast<void*>(si->entry));
		return si->entry;
}

/* Compute the load-bias of an existing executable. This shall only
 * be used to compute the load bias of an executable or shared library
 * that was loaded by the kernel itself.
 *
 * Input:
 *    elf    -> address of ELF header, assumed to be at the start of the file.
 * Return:
 *    load bias, i.e. add the value of any p_vaddr in the file to get
 *    the corresponding address in memory.
 */
static ElfW(Addr) get_elf_exec_load_bias(const ElfW(Ehdr)* elf) {
	ElfW(Addr) offset = elf->e_phoff;
	const ElfW(Phdr)* phdr_table = reinterpret_cast<const ElfW(Phdr)*>(reinterpret_cast<uintptr_t>(elf) + offset);
	const ElfW(Phdr)* phdr_end = phdr_table + elf->e_phnum;

	for (const ElfW(Phdr)* phdr = phdr_table; phdr < phdr_end; phdr++) {
		if (phdr->p_type == PT_LOAD) {
			return reinterpret_cast<ElfW(Addr)>(elf) + phdr->p_offset - phdr->p_vaddr;
		}
	}
	return 0;
}

extern "C" void _start();

/*
 * This is the entry point for the linker, called from begin.S. This
 * method is responsible for fixing the linker's own relocations, and
 * then calling __linker_init_post_relocation().
 *
 * Because this method is called before the linker has fixed it's own
 * relocations, any attempt to reference an extern variable, extern
 * function, or other GOT reference will generate a segfault.
 */
extern "C" ElfW(Addr) __linker_init(void* raw_args) {
	// Initialize static variables.
	solist = get_libdl_info();
	sonext = get_libdl_info();

	KernelArgumentBlock args(raw_args);

	ElfW(Addr) linker_addr = args.getauxval(AT_BASE);
	ElfW(Addr) entry_point = args.getauxval(AT_ENTRY);
	ElfW(Ehdr)* elf_hdr = reinterpret_cast<ElfW(Ehdr)*>(linker_addr);
	ElfW(Phdr)* phdr = reinterpret_cast<ElfW(Phdr)*>(linker_addr + elf_hdr->e_phoff);

	soinfo linker_so;
	memset(&linker_so, 0, sizeof(soinfo));

	// If the linker is not acting as PT_INTERP entry_point is equal to
	// _start. Which means that the linker is running as an executable and
	// already linked by PT_INTERP.
	//
	// This happens when user tries to run 'adb shell /system/bin/linker'
	// see also https://code.google.com/p/android/issues/detail?id=63174
	if (reinterpret_cast<ElfW(Addr)>(&_start) == entry_point) {
		__libc_fatal("This is %s, the helper program for shared library executables.\n", args.argv[0]);
	}

	strcpy(linker_so.name, "[dynamic linker]");
	linker_so.base = linker_addr;
	linker_so.size = phdr_table_get_load_size(phdr, elf_hdr->e_phnum);
	linker_so.load_bias = get_elf_exec_load_bias(elf_hdr);
	linker_so.dynamic = NULL;
	linker_so.phdr = phdr;
	linker_so.phnum = elf_hdr->e_phnum;
	linker_so.flags |= FLAG_LINKER;

	if (!soinfo_link_image(&linker_so, NULL)) {
		// It would be nice to print an error message, but if the linker
		// can't link itself, there's no guarantee that we'll be able to
		// call write() (because it involves a GOT reference). We may as
		// well try though...
		const char* msg = "CANNOT LINK EXECUTABLE: ";
		write(2, msg, strlen(msg));
		write(2, __linker_dl_err_buf, strlen(__linker_dl_err_buf));
		write(2, "\n", 1);
		_exit(EXIT_FAILURE);
	}

	// Initialize the linker's own global variables
	linker_so.CallConstructors();

	// We have successfully fixed our own relocations. It's safe to run
	// the main part of the linker now.
	args.abort_message_ptr = &g_abort_message;
	ElfW(Addr) start_address = __linker_init_post_relocation(args, linker_addr);

	protect_data(PROT_READ);

	// Return the address that the calling assembly stub should jump to.
	return start_address;
}
